The present invention relates to an electrical switching device for switching high voltages in a network having a defined rated voltage, the device including a series connection of at least first and second current interrupters having control elements across which a load voltage is distributed, each interrupter operating according to different quenching principles and exhibiting a different dielectric behavior immediately after a zero passage of load current to be interrupted, the first interrupter exhibiting a steep rate of rise in its dielectric strength with a maximum dielectric strength value which is a fraction of the defined rated voltage, and the second interrupter having a relatively flat rate of rise in dielectric strength compared to the first interrupter with a maximum dielectric strength value which lies above the maximum dielectric strength value of the first interrupter.
Such switches are known in the art as interrupters for direct current circuits. For example, German Offenlegungsschrift [laid-open patent application] No. 2,350,584 discloses a direct current power switching device operating with voltage dividers in which a first power switch, which may be a vacuum switch, is connected in series with a parallel connection of a second power switch, which may be an SF6 gas insulated switch, and an electronic switch. The prior art switching device permits current interruptions which are essentially controlled by the current/voltage characteristic of the electronic switch in conjunction with capacitors connected in parallel with the switches upon the occurrence of a recovery voltage which is greater than the dielectric strength of each one of the two power swithces.
German Offenlegungsschrift No. 3,131,271, discloses a switching system of the interruption of a high voltage direct current comprising a series connection of a vacuum switch and a gas jet switch which are voltage controlled by being connected in parallel with a voltage dependent resistor or capacitor, respectively. This solution utilizes, on the one hand, the capability of vacuum switches to interrupt currents when there is a steep rise in the current and in the recovery voltage and, on the other hand, the capability of the high dielectric strength of an SF6 switch in the low frequency range of the recovery voltage. The two switches open simultaneously and the capacitor connected in parallel with the SF6 switch causes a delayed rise of the recovery voltage across the SF6 switch.
The known switching devices have a relatively complicated configuration because they employ further switching devices and control elements in addition to the two power switches. Moreover, both power switches operate in synchronism and are charged with the same length arc times.
Additionally, German Offenlegungsschrift No. 2,934,776 discloses a medium voltage load break switch composed of a vacuum switching tube and an air break switch. The vacuum switching tube in this case is designed so that it is able to handle recovery voltages occurring during the interruption of operating currents having inductive and capacitive current components, while the air break switch is opened without curent and its separated path merely takes care of the high dielectric stress.